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Reintroducing Object Access Method

The latest z/OS release brings file system support for OAM

The latest z/OS release brings file system support for OAM
Illustration by Dustin Miller

Object Access Method (OAM) has been around for more than two decades, yet has received little recognition for its important role in data storage. It was developed in the late ’80s as a prototype product for an insurance company to replace microfiche and has since evolved into one of the most widely used data-archiving solutions on System z* servers.

OAM is part of DFSMSdfp, a base element of z/OS*, and is typically used for storing archive-type data. OAM stores your object data and also manages the lifecycle of your object data from creation to expiration within a storage hierarchy consisting of multiple levels—disk, optical and tape.

An “object,” which is also called unstructured data, is a named stream of bytes that has no record orientation. OAM views an object as a data stream and no matter what the object contains—company emails, billing statements, medical images—OAM can store any object up to 2000 MB.

The OAM Basics

The original OAM prototype was developed in support of IBM’s optical drives and libraries. The insurance company that first used it wanted to migrate its data off of microfiche and store it on optical, which provided write once, ready many (WORM) capability for compliance. OAM became an official product for other companies to use shortly thereafter.

Erika Dawson, IBM senior technical staff member, said OAM is similar to Tivoli* Storage Manager in that it provides an API that IBM products (e.g., IBM DB2* Content Manager or IBM DB2 Content Manager On Demand) can use to store, retrieve, query, delete and change the way an object is managed. Additionally, customer-written application programs can also use OAM to store object data and manage the data in a storage hierarchy through systems-managed storage (SMS) policies and SMS automatic class selection (ACS) routines. Users can establish policies for object data using SMS ACS routines and OAM will then manage the objects throughout their lifecycle. Used to create backup copies of data, OAM supports a disk layer, optical layer and tape layer from a storage hierarchy perspective. Data is stored to disk using 4 K, 32 K, and large object DB2 tables; metadata for objects is also stored and managed with DB2 tables.

“Initially, we had a disk layer as well as the optical layer,” says Dawson. “Customers, for instance, may have stored an object in our disk layer for six months and then set up policies to then transition the data as it aged maybe six months later to optical. In the mid ’90s we then added a tape layer to OAM so that we support tape devices, both native as well as virtual.”

Caroline Vitse is a freelance writer based in Rochester, Minnesota.


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